It is well documented that many exogenous factors influence the epigenetic control of the growth and differentiation of normal and neoplastic mammary tissue. Recently, protein kinase C, (a Ca2+- and phospholipid-dependent, diacylglycerol-sensitive protein kinase) has been the focus of intensive research and has been implicated to have roles in the control of many cellular processes. The importance of this enzyme system in the regulation of mammary carcinoma growth processes has not been resolved. Thus, the specific aims of this research proposal are the following: 1. To evaluate and characterize the levels, subcellular distribution and biochemical activation of protein kinase C (PK-C) in carcinogen-induced rat mammary carcinomas and in human breast carcinoma cell lines grown as xenografts in athymic mice. 2. To evaluate the potential role of PK-C activation in the control of cell cycle dynamics and cell proliferation in a spontaneously-transformed rat mammary epithelial (RMGE) cell line. Serum components and/or growth factors involved in the observed serum-induced activation of PK-C and DNA synthesis in synchronized RMGE cells will be defined. 3. To evaluate the potential of PK-C in the regulation of mammary (breast) carcinoma proliferation in vitro. The relationship between PK-C activity (subcellular distribution) and the proliferation of cell and organ cultures of rodent and human mammary carcinomas will be examined. Also, the effects of regulators (i.e. activators and inhibitors) of PK-C activity and action on mammary carcinoma cell proliferation will be examined. Mammary cell proliferation will be assessed by measuring changes in cell number over time and the incorporation of 3-H-thymidine into DNA. 4. To evaluate the potential role of PK-C activation in the regulation of mammary carcinoma growth in vivo. PK-C activity will be related to the growth of in situ mammary tumors as influenced by endocrine manipulations.